"John Morrison at the Mount Sinai School of Medicine in New York, US, and colleagues gave injections of the hormone oestrogen to rhesus macaques � which have a menstrual cycle and menopause similar to humans. The monkeys were split into two groups of older and younger animals, and, within these groups, half were given hormone shots � the rest acted as controls."

"On short-term memory tests, the younger animals performed equally well, regardless of whether they received oestrogen or not. But only the older macaques that got the oestrogen boosters performed as well as the younger animals; older untreated monkeys displayed dramatic cognitive decline, the researchers say."

"Autopsies revealed that the oestrogen had affected the neurons in the prefrontal cortex � a region of the brain associated with cognitive tasks."

"The treated monkeys had a higher density of synaptic spines � neural structures that connect brain cells � than the untreated animals. These spines aid brain cell communication, and are critically important for learning and memory, but typically decrease with age."

"Morrison believes oestrogen
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